The widespread use of digital computers and digital data acquisition systems has generated the need for measurement devices having digital-type outputs. A number of digital force sensors exist in the prior art. Resonant force sensors whose frequencies of vibration vary with applied stress are described in U.S. Pat. No. 3,470,400 by Weisbord, U.S. Pat. No. 3,479,536 by Norris, U.S. Pat. No. 4,215,570 by EerNisse, U.S. Pat. No. 4,372,173 by EerNisse and Paros, and U.S. Pat. No. 4,498,344 by Dinger. In order to operate as accurate measurement devices, these resonant sensors must be carefully incorporated into the force-producing structures, as shown in U.S. Pat. No. 4,384,495 by Paros. Also, these sensors operate best in a vacuum or inert atmosphere and thus should be environmentally isolated from the force-producing structures through means as described in U.S. Pat. No. 4,406,966 by Paros. The latter patent also describes means by which the temperature characteristics of a force-sensitive resonator may be improved by combining the inherent temperature sensitivity of the resonator with thermally induced mechanical loads. Temperature-induced errors can be large unless the reactive structural spring rates are low or, as with Dinger (U.S. Pat. No. 4,498,344), the coefficients of thermal expansion are closely matched between the resonator and the structure. Indeed, in U.S. Pat. No. 4,448,546, Paros describes a digital temperature sensor based on thermal mismatch between a resonator and base structure. The foregoing prior art devices suffer from complex and costly arrangements in which environmental errors such as temperature cause large errors. U.S. Pat. No. 4,091,679, by Furusawa et al., discloses an accelerometer having two vibrating quartz resonators coupled to each other which are directly loaded by an inertial mass. The beat frequency between the two resonators is a measure of the applied acceleration.